which third annual Arrowverse crossover event did "Medusa"  features 
"Invasion!"
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Medusa (Supergirl)
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Invasion! (Arrowverse)
52243241
-1
Section::::Abstract.
Invasion! (Arrowverse)
52243241
-1
Section::::Abstract.
Invasion! (Arrowverse)
52243241
-1
Section::::Abstract.
Invasion! (Arrowverse)
52243241